The present invention generally relates to gas-discharge lamps lighting apparatus and, more particularly, to an gas-discharge lamp lighting apparatus for a vehicle or a display of the projection type.
FIG. 17 shows a construction of an gas-discharge lamp lighting apparatus according to the related art disclosed in the Japanese Laid-Open Patent Application 5-166592. FIG. 18 shows a pulse generation circuit of an igniter circuit of the related-art gas-discharge lamp lighting apparatus shown in the above-mentioned Application. Referring to FIGS. 17 and 18, reference numeral 51 indicates an inverter circuit, 52 indicates an igniter circuit, and 52a indicates a pulse generation circuit.
The igniter circuit 52 comprises a pulse generation circuit 52a which generates a pulse, and a pulse transformer PT by which the output of this pulse generation circuit 52a is stepped up. A secondary winding L2 of the pulse transformer PT is connected to a high-pressure gas-discharge lamp Lp in series, and the series circuit composed of the gas-discharge lamp Lp and the secondary winding L2 is connected with both ends of a capacitor C2. The pulse generation circuit 52a shown in FIG. 18 comprises a bi-directional switching element S4 implemented, for example, by a triac, connected to a primary winding L3 of the pulse transformer PT, a trigger element S3 triggering the switching element S4, a trigger circuit causing a breakover of the trigger element S3 and comprising a resistor R2 and a capacitor C4, and a charging circuit comprising a resistor R1 and a capacitor C3 and supplying a dc current to the series circuit composed of the primary winding L3 of the pulse transformer PT and the switching element S4. An AC power is supplied to the pulse circuit 52a via a switch SW. Only when the high-pressure gas-discharge lamp Lp is started, the switch SW supplies AC power to the pulse generation circuit 52a. 
A description will now be given of the operation according to the related art.
In the pulse generation circuit 52a shown in FIG. 18, the capacitor C3 is charged via the resistor R1 when the switch SW is turned on, and the capacitor C4 is charged via the primary winding L3 of the pulse transformer PT and the resistor R2. When the voltage across the capacitor C4 reaches a breakover voltage of the trigger element S3, the electric charge of the capacitor C4 is discharged via the trigger element S3. As a result, a gate current is supplied to the switching element S4 for conduction. When the switching element S4 is turned on, the electric charge built up in the capacitor C3 is discharged via the primary winding L3 and the switching element S4. A high-voltage pulse corresponding to the turn ratio with respect to the primary winding L3 is generated in the secondary winding L2 of the pulse transformer PT. This high-voltage pulse is applied to both ends of the high-pressure gas-discharge lamp Lp via the capacitor C2. The high-voltage pulse is applied to the high-pressure gas-discharge lamp Lp so as to be superimposed on the output of the inverter circuit 51. The high-pressure gas-discharge lamp Lp is ignited by this high-voltage pulse.
Once the high-pressure gas-discharge lamp Lp is started, the switch SW is turned off so that the igniter circuit 52 stops applying the high-voltage pulse to the high-pressure gas-discharge lamp Lp. The output of the inverter circuit 51 keeps the high-pressure gas-discharge lamp Lp lighted in a stable manner.
As described above, the pulse generation circuit, constituting the igniter circuit together with the pulse transformer, comprises the bi-directional switching element, the trigger element that triggers the switching element, the trigger circuit causing a breakover of the trigger element and composed of the resistor R2 and the capacitor C4, and the charging circuit composed of the resistor R1 and the capacitor C3 and supplying a dc current to the series circuit composed of the primary winding of the pulse transformer and the switching element. Accordingly, the number of components constructing the igniter circuit is relatively large. As a result of the large number of components, the cost of the gas discharge lamp lighting apparatus is relatively high and the scale of the device is relatively large.
Accordingly, a general object of the present invention is to provide an gas-discharge lamp lighting apparatus in which the aforementioned problems are eliminated.
Another and more specific object is to provide a small-scale, low-cost gas-discharge lamp lighting apparatus by reducing the number of components constituting an igniter circuit for generating a high-voltage pulse at the discharge starting.
The aforementioned objects can be achieved by an gas-discharge lamp lighting apparatus comprising: power conditioning means regulating a power supplied from a power source, outputting voltages with mutually different levels from two output terminals, and provided with a first capacitor coupled between the two output terminals; a switching circuit unit coupled between the output terminals of the power conditioning means and comprising at least one switching element; and a pulse transformer generating a high-voltage pulse, placed in a circuit connecting the output terminals of the switching circuit unit and an gas-discharge lamp, wherein a first terminal of a primary winding of the pulse transformer is connected to a first output terminal of the power conditioning means via a first output terminal of the switching circuit unit, and a second terminal of the primary winding is directly, or via the switching circuit unit, connected to a second output terminal of the power conditioning means.
The switching circuit unit may comprise one switching element; the first terminal of the primary winding of the pulse transformer may be connected to the second output terminal of the power conditioning means via the one switching element, and the second terminal of the primary winding may be connected to the second output terminal of the power conditioning means, wherein a second capacitor is provided in a circuit connecting the pulse transformer, the gas-discharge lamp and the first output terminal of the power conditioning means, the second capacitor being connected to the gas-discharge lamp in series.
Another switching element may be provided in parallel with the second capacitor.
The switching circuit unit may comprise first and second switching elements, the first terminal of the primary winding of the pulse transformer being connected to the first output terminal of the power conditioning means via the first switching element, and the second terminal of the primary winding being connected to the second output terminal of the power conditioning means via the second switching element, and a second capacitor may be provided in a circuit connecting the pulse transformer, the gas-discharge lamp and the first output terminal of the power conditioning means, the second capacitor being connected to the gas-discharge lamp in series.
A third switching element may be provided in parallel with the second capacitor.
A third capacitor may be connected between a node, connected to the second switching element and the primary winding, and the first output terminal of the power conditioning means.
A parallel circuit formed of a diode and a resistor may be connected between the third capacitor and the node.
A current may be run through the primary winding of the pulse transformer before supplying a current from the second capacitor to the gas-discharge lamp so that a voltage between electrodes of the gas-discharge lamp is larger than a voltage maintained in the second capacitor, and the gas-discharge lamp may be ac driven by alternately performing a current feed from the power conditioning means and a current feed from the second capacitor.
The switching circuit unit may be a full-bridge inverter circuit comprising first through fourth switching elements to convert a dc output voltage of the power conditioning means into an ac voltage, and the first terminal of the primary winding of the pulse transformer may be connected to a first of two switching elements constituting an arm of the switching circuit unit, and the second terminal of the primary winding is connected to a second of the two switching elements constituting the arm.
The gas-discharge lamp lighting apparatus may further comprise initial current feed means supplying a current to the gas-discharge lamp at the discharge starting.
The initial current feed means may comprise a circuit that includes a parallel circuit formed of a resistor and a diode, and a series circuit connecting a fourth capacitor and an inductor.
A third capacitor may be connected between a node, connected to the first of the switching elements and the primary winding, and the first output terminal of the power conditioning means.
A parallel circuit formed of a diode and a resistor may be connected between the third capacitor and the node.
The aforementioned objects can also be achieved by an gas-discharge lamp lighting apparatus comprising: power conditioning means regulating a power supplied from a power source, and outputting voltages with mutually different levels from two output terminals; a switching circuit unit coupled between the output terminals of the power conditioning means and comprising at least one switching element; a capacitor placed in a circuit connecting the output terminals of the switching circuit unit and an gas-discharge lamp; and a pulse transformer connected between the capacitor and the gas-discharge lamp, wherein a first terminal of a primary winding of the pulse transformer is connected to a first electrode of the capacitor, and a second terminal of the primary winding is connected to a second electrode of the capacitor via a switching element, and there is provided a charging circuit for charging the capacitor.
The switching circuit unit may comprise one switching element.
The switching circuit unit may comprise two switching elements.
A current may be run through the primary winding of the pulse transformer before supplying a current from the capacitor to the gas-discharge lamp so that a voltage between electrodes of the gas-discharge lamp is larger than a voltage maintained in the capacitor, and the gas-discharge lamp may be ac driven by alternately performing a current feed from the power conditioning means and a current feed from the capacitor.
A charging circuit switching element may be provided in the charging circuit.